This invention relates to a battery pack which does not use electrical contacts for battery charging, but rather electrical power is transmitted by electromagnetic induction to charge rechargeable batteries contained within the battery pack.
A battery pack attaches in a detachable manner to a portable electrical device, and battery charging can be accomplished with the battery pack attached to the portable electrical device. For example, charging terminals may be exposed from the bottom surface of the attached battery pack. On the other hand, battery pack discharge terminals, which serve to connect the battery pack and the portable electrical device, are internal to the portable electrical device with battery pack attached. However, the portable electrical device attaches to a charging stand and the charging terminals must make electrical contact with supply terminals on that charging stand. Therefore, it is necessary to position the charging terminals where they will always be exposed. For this reason, the charging terminals can be exposed to extremely dirty environments, and this system has the disadvantage that electrical contact problems can easily occur. In particular, for charging stands to discriminate between battery pack types and optimize charging conditions, multiple charging terminals have become common. It is difficult to attach a multiple charging terminal battery pack to a charging stand without developing contact problems on any of the charging terminals. Detrimental effects such as rechargeable battery performance degradation can occur due to charging without good contact at all charging terminals. For example, if the type of rechargeable battery contained in the battery pack is mistaken and charging is performed with large currents, or if charging is performed without correct battery temperature readings, battery performance degradation can occur.
As noted, battery pack charging terminals are exposed when the battery pack is connected to the portable electrical device. Therefore, when portable electrical device is transported in a pocket or a carrying bag, problems such as short circuits can develop due to metallic objects or chains, also transported in the pocket or bag, contacting the charging terminals.
A portable electrical device and charging stand system which charges rechargeable batteries without contacts has been developed to eliminate these problems. In this type of system, a primary coil is housed in the charging stand, and a secondary coil is housed in the portable electrical device. The rechargeable batteries of the battery pack are charged by transmission of electrical power from the primary coil to the secondary coil by electromagnetic induction. The portable electrical device rectifies and converts to direct current (DC) the alternating current (AC) induced in the secondary coil. This DC power is controlled by a control circuit and supplied to the battery pack to charge the rechargeable batteries. The battery pack and portable electrical device are connected by charge-discharge terminals. When battery pack rechargeable batteries are being charged, the portable electrical device is attached to the charging stand. In this configuration, electric power is supplied from the primary coil in the charging stand to the secondary coil in the portable electrical device, secondary coil output is controlled by the control circuit, and power is supplied from the portable electrical device to the battery pack to charge the rechargeable batteries. When the portable electrical device is removed from the charging stand, the battery pack supplies electric power to the portable electrical device allowing it to be operated.
A portable electrical device, which contains a secondary coil and a control circuit, makes externally exposed charging terminals on the attached battery pack unnecessary. This system has the feature that battery pack rechargeable batteries can be charged without electrical contacts with the portable electrical device attached to the charging stand. However, in this type of charging system, the battery pack cannot be charged when it is removed from the portable electrical device. Therefore, this system has the disadvantage that a spare battery pack cannot be attached to the charging stand for charging while the portable electrical device is in use.
Further, in this type of system, it is also necessary to connect the battery pack to the portable electrical device via a control contact. If poor contact occurs at the control contact, it is impossible to correctly charge the rechargeable batteries. Poor contact at the control contact may make it impossible to safely charge the rechargeable batteries or may charge the batteries in a manner resulting in significant battery degradation. This is because the charging circuit housed in the portable electrical device cannot correctly determine battery pack conditions during charging.
This invention was developed to solve these types of problems. Thus it is a primary object of the present invention to provide a battery pack which can charge rechargeable batteries contained inside without provision of charging terminals.
Further, it is another important object of the present invention to provide a battery pack which eliminates improper charging caused by poor electrical contact, and which safely charges the rechargeable batteries contained inside under ideal conditions without battery performance degradation.
The above and further features of the invention will more fully be apparent from the following detailed description and accompanying drawings.